I agree with the two comments above (r6155 and DriveMeNuts).
r6155: Another reason for plugging an internal vent is to avoid the possibility of entrapped material escaping and compromising safety for intrusive inspection. Probably only a real risk if the material is lethal or poisonous...
thread794-25516 and thread794-471960
These threads indicate 'incomplete knowledge' of this subject. I don't claim complete knowledge, and have not here covered everything I know on the topic, but hopefully I have filled in a few gaps. (Now retired, but with more than 41 years experience.)...
